Colorectal cancer remains the second most common cause of cancer-related death in the United States and a significant cause of cancer-related death in other countries as well.1 For decades, the only approved chemotherapeutic drug for treatment of colorectal cancer was 5-fluorouracil (5-FU), and it continues to be the backbone of most first-line chemotherapeutic regimens for patients with advanced disease. However, there has been much progress made in treatment of colorectal cancer in the past decade, with the approval of several new therapeutic agents including irinotecan, oxaliplatin, capecitabine, and most recently, cetuximab and bevacizumab.2,3 Importantly, a variety of new chemotherapeutic regimens utilizing these agents have been devised, which have led to increased response rates and incremental increases in the time to progression and median survival for patients with advanced disease.2,3 Response rates for 5-FU/leucovorin, irinotecan, and oxaliplatin as single agent therapy have been low (23%, 18%, and 12%, respectively), progression-free survival has been short (median 4.0, 4.3, and 4.0 months, respectively), and median survival has also been short, approximately (12, 12, and 14.5 months, respectively).4 With the introduction of 5-FU-based combination chemotherapeutic regimens using irinotecan and oxaliplatin, the response rate has increased substantially, with response rates reported as high as 64% (FOLFOX7), time to progression ranging from 8.9-12.3 months, and median survival now approaching approximately 20 months in some reports.2-4 
Unfortunately, however, these newer combination chemotherapy regimens do have increased toxicity. Regimens containing irinotecan are associated with significant diarrhea and other gastrointestinal toxicity, while those containing oxaliplatin are associated with neurotoxicity.2-10 The neurotoxicity observed is of two types: first, a cumulative and often dose limiting sensory loss with paresthesias that can interfere with function and second, a disturbing cold sensitivity that limits patient acceptance of the FOLFOX regimen.7-10 Thus a drug of comparable efficacy without neurotoxicity would be a welcome substitute for oxaliplatin in combination with 5-FU and leucovorin.
Picoplatin is a platinum analogue that has demonstrated synergy with 5-FU in vitro in pre-clinical studies and has undergone extensive Phase 1 and 2 testing in a variety of cancers.11-22 Like other platinum analogues, picoplatin causes cell death by the formation of covalent cross-links in DNA that interfere with DNA replication and transcription, leading to cell death. Cisplatin, the first platinum analogue, was introduced approximately 20 years ago and is still widely used. The approval of cisplatin was followed by approval of carboplatin, and most recently by that of oxaliplatin.
Treatment with platinum analogues is limited by their toxicity. While neurotoxicity and nephrotoxicity are the main dose-limiting toxicities (DLT) observed following cisplatin treatment, myelosuppression is most significant following carboplatin treatment. Carboplatin is known to cause cumulative dose-related toxicity that results in slow bone marrow recovery. Peripheral neurotoxicity is well documented in patients treated with oxaliplatin. The unacceptable nephrotoxicity, oto-, and neurotoxicity associated with earlier platinum analogues has not been reported with picoplatin either in animal studies or in clinical trials.11,19-22 
The efficacy of platinum analogues is also limited by several (intrinsic or acquired) mechanisms of resistance, including impaired cellular uptake, intracellular inactivation by thiols [e.g., reduced glutathione], and enhanced DNA repair and/or increased tolerance to platinum-DNA adducts.23 Pre-clinical studies indicate that picoplatin can overcome these three mechanisms of resistance. This has been demonstrated in vitro and by using human ovarian xenograft tumor models that exhibit resistance to cisplatin.13-17 Several human ovarian and colon cell lines with induced resistance to oxaliplatin retain sensitivity to picoplatin.16-18 
In Phase 1 studies, indications of activity were seen in subjects with ovarian cancer, non-small cell lung cancer (NSCLC), small cell lung cancer (SCLC), head and neck cancer, renal cell cancer, thymic cancer, pancreatic cancer, stomach cancer, leiomyosarcoma, liver cancer, mesothelioma, and prostate cancers.24,25 In Phase 2 studies, indications of efficacy were seen in subjects with ovarian, NSCLC, SCLC, mesothelioma, prostate cancer, and breast cancer.
Picoplatin and processes for making picoplatin and for using picoplatin in treatment are disclosed and claimed in U.S. Pat. Nos. 5,665,771 (issued Sep. 9, 1997), and 6,518,428 (issued Feb. 11, 2003), and in PCT/GB0102060, filed May 10, 2001, published as WO2001/087313, which are incorporated herein by reference in their entireties.
About 40% of patients with mCRC have K-ras mutations and their mCRC does not respond to epidermal growth factor receptor (EGFR) inhibitors such as cetuximab and panitumumab. Many cetuximab-treatment studies in mCRC demonstrated very low or even zero response rates, short progression-free survival, and short overall survival in K-ras mutation positive mCRC. Because K-ras wild type CRC patients treated with EGFR inhibitors have significantly higher objective response rates, increased progression-free survival, and increased overall survival, K-ras testing is now used in routine clinical practice to select the subset of mCRC patients most likely to benefit from treatment with an EGFR inhibitor. Subset selection spares patients who are unlikely to respond to EGFR inhibitors for side effects and the cost of an ineffective drug. Examples of companies that offer K-ras testing to medical oncologists include:
For example, see: M. Brink et al., Carcinogenesis. 2003; 24:703-10; A. Lièvre et al., J Clin Oncol. 2008; 26:374-9; W. De Roock et al., Ann Oncol. 2007, Nov. 12; F. Di Fiore et al., Br J Cancer. 2007; 96:1166-9; A. Lièvre et al., Cancer Res. 2006; 66:3992-5; C. S. Karapetis et al., NEJM. 2008; 359 (N 17):1757-1765; Amado et al., 2008 American Society of Clinical Oncology Gastrointestinal Cancers Symposium, Abstract 278.
Picoplatin (SP-4-3) (cis-aminedichloro(2-methylpyridine)Pt(II)), and useful prodrugs and analogs thereof are disclosed in U.S. Pat. Nos. 5,665,771; 6,518,428; 6,413,953 and PCT/GB/01/02060.